In the formation of glassware it has been common practice to form a blank, or parison, in a parison molding portion of the glassware molding machine, to automatically transfer the parison to a blowing molding portion of the glassware molding machine, and then to blow mold the parison into conformity to a blow mold.
In this prior art practice, the parison is commonly formed by a plunger which forms the internal surface and two separate molding portions which may have more than one part which form the external surface. The construction of these molds and their functions typically are as follows:
One of these molding portions forms the body of the parison, which is the portion of the parison that later will be blow molded. This body molding portion typically includes two sidewall mold halves that are transversely movable to open and closed positions about a central axis and are frequently referred to as the blank molds. It also incudes a bottom surface mold referred to as the baffle. The baffle mold is movable into and out of engagement with the blank mold halves to allow loading of the glass job into the inverted blank mold before forming of the parison.
Another of these molding portions forms the neck of the parison which is molded to its final size and shape, as contrasted to the body of the parison which subsequently is blow molded into its final size and shape. This neck molding portion includes two sidewall mold halves that are transversely movable to open and closed positions about a central axis and are frequently referred to as the neck rings. It also includes a top surface mold frequently referred to as the finish guide plate.
The top finish mold provides a top sealing surface to the container that is unmarred by a longitudinal seam, whereas the neck ring mold, being formed in two halves, leaves a seam line on that portion of the parison that is formed within the neck ring portions.
After the parison is formed by thse two molding portions and the parison plunger, the parison, which is still retained within the neck ring, is transported to a blow molding portion of the individual section glassware molding machine. Typically the parison is molded with the neck ring at the bottom of the parison; and a neck ring holder transports the parison to the blow mold portion of the machine by swinging the parison upwardly in a one hundred eighty degree arc, and places it in an upright position in a blow molding station.
There are several disadvantages and problems that are inherent in machines that are constructed as noted above. One of the inherent problems is that there are conflicting requirements for the physical properties of the parison.
The neck portion of the parison must be sufficiently cool to provide the physical properties that will enable transporting the body portion of the parison to the blow mold and to retain the dimensional requirements of the finished container. And yet, the body portion of the parison must be sufficiently hot and plastic to enable it to be blow molded to the size and shape of the finished container.
Further, the body portion of the parison must be sufficiently cool to provide the physical properties that can resist acceleration, deceleration, and centrifugal forces on the body portion during transport from the parison molding portion to the blow molding portion of the machine. And yet, the body portion must be sufficiently hot and plastic to enable it to be blow molded to the size and shape of the finished container.
These mutually contradictory temperature and physical requirements for the parison have resulted in unduly long cycle times for glassware molding machines of this type because of the need for a reheat cycle that has been interposed between the parison molding step and blow molding step. This reheat cycle, at the expense of production rate, has reheated and resoftened the body portion of the parison after transporting the parison to the blow molding portion of the machine.
However, distortions in the parison, as caused by forces imposed on the parison during transport, have not been corrected by reheating; and these distortions in the parison have resulted in glassware that is uneven in thickness, that is easily broken, and/or in glassware that fractures during blow molding, or in subsequent handling thereof. In order to obtain sufficient strength in the finished product, it has been necessary to design glassware with thicknesses that are excessive from the standpoint of the raw materials required, the heat required for melting, shipping costs of finished containers to food processors, and shipping costs of filled containers to consumers.
Another problem that typically has plagued machines of the prior art type is that the parison blank molds have been made in two separable halves; and so the parison typically has had a seam line, a difference in thickness in circumferentially different portions of the parison, and a sudden change at the same line due to temperature differences caused by the mold discontinuities.
In addition, machines of the type described have not provided god radial alignment between the parison plunger and the parison neck molds. This misalignment, together with the above-noted problems of the blank mold halves, has caused unequal wall thickness in the parison; and this unequal wall thickness in the parison has caused excessive losses in manufacturing, excessive thick wall designs for containers, excessive cost for glass raw materials, excessive costs for thermal energy in manufacturing, and excessively high costs for shipping.
The failure of machines as described above to provide good radial alignment has also resulted in excessive wear between the parison neck mold parts and the parison plunger, at times even resulting in particles of metal being sheared off of either the parison plunger or the neck mold parts, and thereby resulting in particles of metal being molded into the parison.
Another cause of impurities has been the method of forming the parison in an inverted position. In typical constructions, the parison plunger enters the parison mold from below, and a gob of molten glass is dropped into an opening in the top of the inverted parison blank mold; so that contamination particles in the environment can drop directly onto the parison plunger.
Another disadvantage of the prior machines is that it has been common practice to deposit finished glassware onto a dead plate and then to slide the finished glassware onto a conveyor. This extra step in the process results in damage to the outside container surfaces, lowering container strength and causing breakage of containers in handling and in filling and processing of products in the containers.
Another problem with machines as described above has been an excessively large number of adjustments that are required either for changing from one size of container to another, for obtaining and maintaining alignment of machine elements, and for changes required to achieve an acceptable transfer of the parison to the blow mold. Typically, there have been over ten different types of adjustments related to merely change from molding one size of container to another size.
Finally, because of the contradictory requirements for physical strength and plasticity in the parison, for frequent adjustments needed for acceptable parison transfer, the readjustments needed after initial heating of molds and for frequent adjustments needed for delicate gob loading, it has taken an excessive number of hours of continuous running of a given mold before the percentage of rejects drops to an acceptable level.
There have been attempts in the prior art to overcome the difficulties and disadvantages of machines of the type described above; but all such attempts have fallen short for optimizing advantages and minimizing disadvantages.
The prior art discloses glassware forming devices, especially of the paste mold type, that provide for maintaining a fixed, axial alignment of the parison plunger and neck ring mold for parison forming and the blow mold for finished article forming. For example U.S. Pat. No. 3,142,552 to Martin discloses generally such a forming means wherein the parison is not transferred until after it is blow molded into the finished article. Although said apparatus of Martin is satisfactory for making paste moldings for seamless glass articles, such an apparatus is not practical nor economical because of its speed limitations for high production of commercial glass containers including wide mouth food jars and the like. Another glassware forming device that provides a vertical alignment of the blank mold and neck ring mold for parison forming and the blow mold for finished article forming is disclosed in U.S. Pat. No. 4,002,449 to Martin. In the device of Martin, two interconnected sets of blow molds and neck rings are employed to oscillate between the forming position and the take-out position, and single sets of blank molds and plungers are moved into and out of the forming position in timed relation therewith. While there are some advantages to the machine which is disclosed by Martin, one obvious limitation of his design is in the oscillating movement and the inherent difficulty of providing precise alignment between the parison plunger, which is fixed with regard to a single actuating axis, and the oscillating neck ring assemblies. Another apparent disadvantage with his machine is that the motions of the two neck ring and blow mold assemblies are tied together; so the machine is inherently slow because cycle time economies cannot be achieved by timing motions according to the needs of each step in the process.
For an effective and economical manufacture of glass containers such as used in the food packaging industry, it would be highly desirable to have a forming machine combining the features of single station forming of parison and finished containers with an upright solid blank, precision alignment of plunger and neck ring mechanisms, and high-speed, damage-free transfer from the forming station, a combination of features for a glass-forming machine not found in the prior art.
Therefore, it is a primary object of the invention to form the parison an then to form the finished container without moving the parison from one axis to another, thereby minimizing distortion to the parison, eliminating handling damage of the parison, reducing the time required to reheat the parison, reducing the scrap rate of blow molding distorted parisons and parisons with surface damage, and increasing the production rate.
It is another primary object of the invention to provide superior alignment between the parison plunger and the neck ring assembly, thereby achieving improved uniformity in wall thicknesses of the parisons, eliminating wear between the parison plunger and neck mold assembly, reducing parison contamination from wear particles, and increasing the strength of the formed glassware through better uniformity of the parisons and less contamination in the glass.
It is another primary object of the invention to use two body forming mold assemblies for a single parison forming assembly and to independently time the movement of the body forming assemblies between a forming station and a cooling and take-out station, thereby increasing the production rate.
It is another primary object of the present invention to provide a glassware molding machine in which the number of adjustments that are required to change from one job to another, and time that is required to achieve optimum running conditions and a minimum scrap rate, are both reduced.
It is another object of the invention to eliminate the blowhead portion of the body molding assembly, to replace the blowhead with an integrated body molding mechanism, to vacuum form the completed containers, and to provide an internal cooling device that does not touch the body forming molds, thereby eliminating mismatching of the forming mold portions, and eliminating cracks and broken glassware that are caused by excessive forming pressures.
It is another object of the invention to provide a take-out mechanism that will take the finished containers from the body forming mold with controlled acceleration forces, and that will deposit the finished article onto a conveyor with an optimized distance between containers, thereby minimizing handling damage and minimizing damage from containers rubbing together.
It is an object of the present invention to reduce container glass weight and to improve container wall strength: by minimizing contamination of the parison from particles sheared or worn from the parison plunger and neck molds through misalignment of these parts, by minimizing surface damage to the parison from contamination of the parison, by minimizing variations in wall thicknesses of the parisons through improved concentricity of parison plunger and neck molds, by minimizing variations in wall thicknesses of the parisons through the use of a one-piece parison blank mold, by minimizing handling damage and distortion to the parison prior to body molding, by minimizing handling damage of the finished container, and by minimizing variations in the wall thickness of the finished container.
Finally, it is an object of the present invention to reduce the costs of raw materials, thermal energy and shipping by strengthening the walls of the container, by achieving better uniformity in the wall thicknesses of the containers, and by a subsequent reduction in wall thicknesses of the containers.